Attempt to index nil with FindFirstChildWichIsA?

I want to make a custom key to drop tools, and everything works fine on the ClientSide of things and an event is fired, but the actual serversided drop script seems to not work, I can't find why, I tried to make char's "Archivable" value true but it gave a different error, here take a look.

local dropEvent = game.ReplicatedStorage.DropEvent

function onPlayerAdded(plr)
    local char = plr.Character

    local function dropItem()
        local tool = char:FindFirstChildWhichIsA("Tool")
        tool.Parent = game.Workspace
    end
    dropEvent.OnServerEvent:Connect(dropItem)
end

game.Players.PlayerAdded:Connect(onPlayerAdded)

The output was: ServerScriptService.Script:7: attempt to index nil with 'FindFirstChildWhichIsA'

Help would be appreciated, thanks.